defusedxml
html.entities — HTML 一般实体的定义
html.entities
源代码： Lib/xml/
Python’s interfaces for processing XML are grouped in the xml 包。
xml
警告
The XML modules are not secure against erroneous or maliciously constructed data. If you need to parse untrusted or unauthenticated data see the XML vulnerabilities and The defusedxml Package 章节。
It is important to note that modules in the xml package require that there be at least one SAX-compliant XML parser available. The Expat parser is included with Python, so the xml.parsers.expat module will always be available.
xml.parsers.expat
The documentation for the xml.dom and xml.sax packages are the definition of the Python bindings for the DOM and SAX interfaces.
xml.dom
xml.sax
The XML handling submodules are:
xml.etree.ElementTree : the ElementTree API, a simple and lightweight XML processor
xml.etree.ElementTree
xml.dom : the DOM API definition
xml.dom.minidom : a minimal DOM implementation
xml.dom.minidom
xml.dom.pulldom : support for building partial DOM trees
xml.dom.pulldom
xml.sax : SAX2 base classes and convenience functions
xml.parsers.expat : the Expat parser binding
The XML processing modules are not secure against maliciously constructed data. An attacker can abuse XML features to carry out denial of service attacks, access local files, generate network connections to other machines, or circumvent firewalls.
The following table gives an overview of the known attacks and whether the various modules are vulnerable to them.
kind
sax
etree
minidom
pulldom
xmlrpc
Vulnerable (1)
DTD retrieval
Vulnerable
Vulnerable (6)
Expat 2.4.1 and newer is not vulnerable to the “billion laughs” and “quadratic blowup” vulnerabilities. Items still listed as vulnerable due to potential reliance on system-provided libraries. Check pyexpat.EXPAT_VERSION .
pyexpat.EXPAT_VERSION
xml.etree.ElementTree doesn’t expand external entities and raises a ParseError when an entity occurs.
ParseError
xml.dom.minidom doesn’t expand external entities and simply returns the unexpanded entity verbatim.
xmlrpc.client doesn’t expand external entities and omits them.
xmlrpc.client
Since Python 3.7.1, external general entities are no longer processed by default.
Expat 2.6.0 and newer is not vulnerable to denial of service through quadratic runtime caused by parsing large tokens. Items still listed as vulnerable due to potential reliance on system-provided libraries. Check pyexpat.EXPAT_VERSION .
The Billion Laughs attack – also known as exponential entity expansion – uses multiple levels of nested entities. Each entity refers to another entity several times, and the final entity definition contains a small string. The exponential expansion results in several gigabytes of text and consumes lots of memory and CPU time.
A quadratic blowup attack is similar to a Billion Laughs attack; it abuses entity expansion, too. Instead of nested entities it repeats one large entity with a couple of thousand chars over and over again. The attack isn’t as efficient as the exponential case but it avoids triggering parser countermeasures that forbid deeply nested entities.
Entity declarations can contain more than just text for replacement. They can also point to external resources or local files. The XML parser accesses the resource and embeds the content into the XML document.
Some XML libraries like Python’s xml.dom.pulldom retrieve document type definitions from remote or local locations. The feature has similar implications as the external entity expansion issue.
Decompression bombs (aka ZIP bomb ) apply to all XML libraries that can parse compressed XML streams such as gzipped HTTP streams or LZMA-compressed files. For an attacker it can reduce the amount of transmitted data by three magnitudes or more.
Expat needs to re-parse unfinished tokens; without the protection introduced in Expat 2.6.0, this can lead to quadratic runtime that can be used to cause denial of service in the application parsing XML. The issue is known as CVE-2023-52425 .
The documentation for defusedxml on PyPI has further information about all known attack vectors with examples and references.
defusedxml is a pure Python package with modified subclasses of all stdlib XML parsers that prevent any potentially malicious operation. Use of this package is recommended for any server code that parses untrusted XML data. The package also ships with example exploits and extended documentation on more XML exploits such as XPath injection.
xml.etree.ElementTree — ElementTree XML API
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